O2 partial pressure
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greg somers
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The air that we breathe is 1 atm (atmoshpere) at 14.7 psi.
It is made up of approx 79% nitrogen,20% oxygen and 1% trace gases.The total pressure of all the gases is 100%.
Because oxygen is only 20% of the total pressure,we can still measure it by saying it is partial pressure of the whole.
As to how it works in dive mixed gas as follows.
If you take 5 x 20% partial pressure of oxygen then you get 1 whole or 100% oxygen.That's what happens to us when we dive at normal air at 5 atms or 40 metres.
However,due to the problem of oxygen toxicity which according to the agencies should have a partial pressure no higher than 1.4 -1.6 atms (60 - 70m normal air),it means that when we use nitrox with a higher oxygen content we must calculate the new partial pressure and cannot dive as deep as air.
EAN 32 becomes 32% partial pressure per atm,EAN 36 becomes 36%.
Take EAN 36 for instance.....
3 x 36% = 108 % or 1.08 atms partial pressure.So,at 30m you will look at 4 x 36% = 1.44 atm partial pressure Oxygen which is at the limit you should go on EAN36.
The benefits of nitrox is that you get more oxygen and less nitrogen absorbtion,so your surface time between dives can be dramatically reduced,which is good for multiple dives.Also with the nitrox you may get less tired and recover fatigue-wise quicker.
The down side is reduced depth.
Also you must have a special tank set aside because the tank must be specially cleaned to handle increased oxygen rates and filling with normal air will ruin the clean and it needs to be done again.
That's partial pressures in a nutshell and it should have been covered as one of your 4 basic laws of physics that affect diving during your training.Check your training manual.
Hope that's clear enough for you.
Cheers my little sautee'd green-legged one...
The Gasman.
Hope that
It is made up of approx 79% nitrogen,20% oxygen and 1% trace gases.The total pressure of all the gases is 100%.
Because oxygen is only 20% of the total pressure,we can still measure it by saying it is partial pressure of the whole.
As to how it works in dive mixed gas as follows.
If you take 5 x 20% partial pressure of oxygen then you get 1 whole or 100% oxygen.That's what happens to us when we dive at normal air at 5 atms or 40 metres.
However,due to the problem of oxygen toxicity which according to the agencies should have a partial pressure no higher than 1.4 -1.6 atms (60 - 70m normal air),it means that when we use nitrox with a higher oxygen content we must calculate the new partial pressure and cannot dive as deep as air.
EAN 32 becomes 32% partial pressure per atm,EAN 36 becomes 36%.
Take EAN 36 for instance.....
3 x 36% = 108 % or 1.08 atms partial pressure.So,at 30m you will look at 4 x 36% = 1.44 atm partial pressure Oxygen which is at the limit you should go on EAN36.
The benefits of nitrox is that you get more oxygen and less nitrogen absorbtion,so your surface time between dives can be dramatically reduced,which is good for multiple dives.Also with the nitrox you may get less tired and recover fatigue-wise quicker.
The down side is reduced depth.
Also you must have a special tank set aside because the tank must be specially cleaned to handle increased oxygen rates and filling with normal air will ruin the clean and it needs to be done again.
That's partial pressures in a nutshell and it should have been covered as one of your 4 basic laws of physics that affect diving during your training.Check your training manual.
Hope that's clear enough for you.
Cheers my little sautee'd green-legged one...
The Gasman.
Hope that
Iguana Don
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Frog,
"The total pressure exerted by a mixture of gasses is equal to the sum of the pressures of each of the different gases making up the mixture--each gas acting as if it alone were present an occupied the total volume."---Doolin Dalton
What this means in laymans terms is, each gas within a mixture acts independently of the others. The individual pressure exerted by a particular component of the gas mixture in proportional to the number of molecules of that particular gas within the mixture. This individual pressure exerted by a component gas in referred to as a partial pressure.
Hope this helps
As you progress in your diving, you will learn this law and many others that apply to scuba diving.
ID
"The total pressure exerted by a mixture of gasses is equal to the sum of the pressures of each of the different gases making up the mixture--each gas acting as if it alone were present an occupied the total volume."---Doolin Dalton
What this means in laymans terms is, each gas within a mixture acts independently of the others. The individual pressure exerted by a particular component of the gas mixture in proportional to the number of molecules of that particular gas within the mixture. This individual pressure exerted by a component gas in referred to as a partial pressure.
Hope this helps
As you progress in your diving, you will learn this law and many others that apply to scuba diving.
ID
keralucu
Senior Member
... Gasman, do you think you could make that a little MORE complex please? Just in case some of us whose brains are not working that well this week aren't confused enough... ID - thanks for the briefer explanation, although I don't know about 10 words or less! (Nor about it actually being any clearer - but that's just me...)
Ta.
Oh its alot more simple than i had thought.
So basically all i do is multiply the depth by the oxygen concentration (percent units). Thanks for the explanation guys.
PS: Where (in the PADI regime) was i supposed to learn about this?
PSS: Something they never taught me which i definately want to know is how to hyperventilate so i can stay underwater longer when skindiving.
So basically all i do is multiply the depth by the oxygen concentration (percent units). Thanks for the explanation guys.
PS: Where (in the PADI regime) was i supposed to learn about this?
PSS: Something they never taught me which i definately want to know is how to hyperventilate so i can stay underwater longer when skindiving.
Sue
Guest
Frog
Unless you take the Nitrox course you won't learn about PPO2 with PADI. But for technical training I would advise TDI http://www.tdisdi.com .Despite the fact that I've done OW and AOW and am into PADI rescue right now, I've done a few tech courses with TDI and am quite pleased.
If you're interested about this subject there's a lot of reading on internet, just search under Nitrox, technical diving or Oxygen - email me if you want a few links
Cheers
Sue
Unless you take the Nitrox course you won't learn about PPO2 with PADI. But for technical training I would advise TDI http://www.tdisdi.com .Despite the fact that I've done OW and AOW and am into PADI rescue right now, I've done a few tech courses with TDI and am quite pleased.
If you're interested about this subject there's a lot of reading on internet, just search under Nitrox, technical diving or Oxygen - email me if you want a few links
Cheers
Sue
Iguana Don
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It's taught in the Divemaster class, you don't have to even be nitrox certified to learn this and all the other Laws.
Dalton, Boyle, Henry & Charles
Hyperventilation is taught in the skindiving part of Open water, but many don't teach it. It's an option to instructors.
ID
Dalton, Boyle, Henry & Charles
Hyperventilation is taught in the skindiving part of Open water, but many don't teach it. It's an option to instructors.
ID
Not quite!!!!!!!
ppO2 at 10m = 21% of 2 atmospheres
You forgot to add 1 (due to atmospheric pressure)
so the real formula for the people that work in bars and metres is
(%value / 100) x ((depth/10)+1) =pp(whatever gas you have the % of)
Sorry about all the brackets, but I can't get an equation here easily.
In the PADI regime it is mentioned in the encyclopedia I think, so you come across it at DM level, or as sue mentioned, in the Nitrox course.
As for hyperventilating, DON'T. This causes shallow water blackout! Breath deeply 3 or 4 times maximum. Any more is not good for you. In the Padi manual it sais 'correct hyperventilation'. There is a very fine line between improved skin diving, and dangerous levels of hyperventilation.
Jon T
In other words Jon it is...
the pressure at a given depth (in atmmospheres) multiplied by the oxygen concentration of the gas (in percent) divided by 100?
As Greg said:
--at 30 metres for EAN 36--
4 x 36 = 144/100 = 1.44
So what is the accepted pp for 02 (maximum?) before O2 toxicity kicks in?
Does anyone know where i can see the nitrox tables on the net? Cheers
PS: thanks to everyone for there help on this. Sue dont worry, i am serious about diving and as such i will never take a PADI course now i have AOW. All other certs will be from IANTD and GUE.
the pressure at a given depth (in atmmospheres) multiplied by the oxygen concentration of the gas (in percent) divided by 100?
As Greg said:
--at 30 metres for EAN 36--
4 x 36 = 144/100 = 1.44
So what is the accepted pp for 02 (maximum?) before O2 toxicity kicks in?
Does anyone know where i can see the nitrox tables on the net? Cheers
PS: thanks to everyone for there help on this. Sue dont worry, i am serious about diving and as such i will never take a PADI course now i have AOW. All other certs will be from IANTD and GUE.
calculation correct! - gasman gave it to you in a very strange way - I tried something easier.
ppO2 being bad (if you listen to the US diving agencies) is 1.6 French divers use 1.9, and the US navy for many years use a ppO2 of 2.0 for 100% O2 decompression.
Before you totally give up on the recreational agencies, remember, that is what they are. They are recreational, they are designed for people to have fun, relatively safely. Equally, don't become one of the annoying DIR fanatics that disparages anyone who doesn't do DIR, even on simple open water dives. Everything has its place in the grand scheme of things, equally, people like GUE demand a large number of dives to START their courses (100 minimum?), in many ways it is worth putting yourself through the PADI rescue / DM courses whilst you get to this 100 figure. You do learn a lot about responsibility from these, and they will improve you as a diver, such that you are fit to start with these other agencies.
Just .02
Jon T
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